Clue to origin of cosmic rays

Ken Kola, 15th February 2013

Astronomers believe they've now worked out the details of how supernova remnants can form cosmic rays.

In 1006, a new star was seen in the southern skies that was many times brighter than Venus; maybe almost as bright as the moon. It was so bright at maximum that it cast shadows and it was visible during the day.

More recently, astronomers identified the site of this supernova and named it SN 1006. They have also found a glowing and expanding ring of material in the southern constellation of Lupus that constitutes the remains of the vast explosion.

It's long been suspected that such supernova remnants may also be where some cosmic rays — very high energy particles originating outside the solar system and travelling at close to the speed of light — are formed. But until now the details of how this might happen were a mystery.

Now, a team from the Max Planck Institute for Astronomy has used the VIMOS instrument on the Very Large Telescope to study the 'shock front' - the region where high-speed material ejected by the supernova ploughs into the stationary interstellar matter.

They've built up a map of the properties of the gas, and how these properties change across the shock front.

And the results were a surprise, suggesting that there were many very rapidly moving protons in the gas in the shock region. While these aren't the cosmic rays themselves, they could be the necessary 'seed particles' which interact with the shock front material to reach high energies and fly off into space as cosmic rays.

"This is the first time we were able to take a detailed look at what is happening in and around a supernova shock front," says Sladjana Nikolić.

"We found evidence that there is a region that is being heated in just the way one would expect if there were protons carrying away energy from directly behind the shock front."